Belgian drugs, chemicals and plastics maker Solvay said on Monday it would sell its drugs unit to U.S. partner Abbott Laboratories for 4.5 billion euros ($6.5 billion) in cash and reinvest in chemicals and plastics.

Abbott had agreed to buy the unit to bolster its flagging prescription drug business by giving it a number of new medicines in late-stages of testing, sources familiar with the deal had earlier told Reuters.

We are building a new refocused group with the financial means to further accelerate sustainable growth, Solvay's board chairman Alois Michielsen said in a statement.

The enterprise value of the deal is 5.2 billion euros, including 4.5 billion in cash, additional potential milestone payments of up to 300 million euros between 2011 and 2013 and liabilities of about 400 million euros.

Solvay said the proceeds from the deal will be reinvested in external and organic growth in strategic projects in chemicals and plastics with a sharp focus on long term value creation.

Studies about such reinvestments are ongoing, it added.

(Reporting by Aaron Gray-Block)